This invention relates to the fabrication of III-V and II-VI compound semiconductor devices and, in particular, to the formation of desirable coatings on the surface of said devices.
The use of III-V and II-VI compound semiconductors to form devices such as light emitting diodes (LEDs), lasers, and photodiodes is continuing to expand. One of the critical steps in the fabrication of such devices is the formation of localized p-n junctions and ohmic contacts by diffusion of material into the semiconductor surface. Such diffusions require a mask which does not interact with the semiconductor, which is impermeable to the diffusing species and which remains intact at high temperatures. In some processing, it is also important to anneal the devices at high temperature. During such an annealing, the device is usually encapsulated with a coating to avoid thermal decomposition of the semiconductor. This coating must also remain intact and not interact with the semiconductor even at high temperatures.
In the fabrication of III-V and II-VI compound devices, silicon dioxide or silicon nitride is typically used as a diffusion mask or encapsulation coating. While generally adequate, use of such layers produces problems in reproducibility since the stoichiometry and physical properties of these films can vary depending on deposition conditions. Further, the thermal coefficient of expansion of these films differs greatly from that of the semiconductor, thereby causing stresses which can crack the coating during thermal treatments and can cause undesired lateral diffusion of the impurity in the semiconductor surface.
It is therefore an object of the invention to provide a coating for III-V and II-VI compound semiconductors, which coating is highly reproducible and has a close thermal expansion match with the semiconductor.